Crosslinked emissive layer containing quantum dots for light-emitting device and method for making same

ABSTRACT

A light-emitting device includes an anode; a cathode; and an emissive layer disposed between the anode and the cathode, the emissive layer including quantum dots dispersed in a crosslinked matrix formed from one or more crosslinkable charge transport materials. A method of forming the emissive layer of a light-emitting device includes depositing a mixture including quantum dots and one or more crosslinkable charge transport materials on a layer; and subjecting at least a portion of the mixture to UV activation to form an emissive layer including quantum dots dispersed in a crosslinked matrix.

RELATED APPLICATION DATA

The application is a continuation-in-part of U.S. patent applicationSer. No. 15/937,073, filed Mar. 27, 2018, the disclosure of which isherein incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates to light-emitting devices, and in particular tolight-emitting devices including a crosslinked emissive layer containingnanoparticles. The light-emitting devices may be implemented in displayapplications, for example high resolution, multicolor displays. Theinvention further relates to methods of manufacturing saidlight-emitting devices.

BACKGROUND ART

A common architecture for a light-emitting device includes an anode,which acts as hole injector; a hole transport layer disposed on theanode; an emissive material layer disposed on the hole transport layer;an electron transport layer disposed on the emissive material layer; anda cathode, which also acts as electron injector, disposed on theelectron transport layer. When a forward bias is applied between theanode and cathode, holes and electrons are transported in the devicethrough the hole transport layer and electron transport layer,respectively. The holes and electrons recombine in the emissive materiallayer, which emits light.

When the emissive material layer includes an organic material, thelight-emitting device is referred to as an organic light emitting diode(OLED). When the emissive material layer includes nanoparticles,sometimes known as quantum dots (QDs), the device is commonly calledeither a quantum dot light emitting diode (QLED, QD-LED) or anelectroluminescent quantum dot light emitting diode (ELQLED).

In order to include QLEDs in multicolor high-resolution displays,different manufacturing methods have been designed. These methods arebased on disposing three different types of QDs in three differentregions of a substrate such that they emit (through electricalinjection, i.e., by electroluminescence) at three different colors: red(R), green (G), and blue (B). Sub-pixels that respectively emit red,green, or blue light may collectively form a pixel, which in-turn may bea part of an array of pixels of the display.

U.S. Pat. No. 7,910,400 (Kwon et al., published Mar. 22, 2011) describesthat QD films can be made more uniform using wet-type film exchangingligand processes where QDs can be connected to each other using organicligands with particular functional groups at both ends (e.g. thiol,amine, carboxyl functional groups).

United States Patent Application Publication No. US 2017/0155051 (TorresCano et al., published Jun. 1, 2017) describes that QDs can besynthesized with polythiol ligands, and can lead to better packing whendeposited and further cured by thermal processes.

International Application Publication No. WO 2017/117994 (Li et al.,published Jul. 13, 2017) describes that through an external energystimuli (e.g. pressure, temperature or UV irradiation) QDs which emitdifferent colors can be selectively attached to bonding surfaces.Surfaces and ligands of QDs must contain particular ending functionalgroups (e.g. alkenes, alkynes, thiols) in order to be selectivelystrongly bonded to each other through chemistry reactions.

This concept is further expanded in International ApplicationPublication No. WO 2017/121163 (Li et al., published Jul. 20, 2017),where QDs with R, G and B emission colors can be patterned separatelyusing cross-linkable ligands and organic connectors through chemistryreactions that are activated selectively with UV radiations at differentmonochromatic wavelengths.

Park et al., Alternative Patterning Process for Realization ofLarge-Area, Full-Color, Active Quantum Dot Display, Nano Letters, 2016,pages 6946-6953 describes that QDs with R, G and B emission colors arepatterned combining conventional photolithography and layer by layerassembly. QD layers are deposited selectively on activated (charged)surfaces.

CITATION LIST

-   U.S. Pat. No. 7,910,400 (Kwon et al., published Mar. 22, 2011).-   US 2017/0155051 (Torres Cano et al., published Jun. 1, 2017).-   WO 2017/117994 (Li et al., published Jul. 13, 2017).-   WO 2017/121163 (Li et al., published Jul. 20, 2017).-   Park et al., Alternative Patterning Process for Realization of    Large-Area, Full-Color, Active Quantum Dot Display, Nano Letters,    2016, pages 6946-6953.

SUMMARY OF INVENTION

In order to fabricate high resolution displays, light-emitting devicesincluding quantum dots (QDs) that emit different colors need to beselectively deposited in certain patterns (e.g., sub-pixelarrangements). In accordance with the present disclosure, methods ofproducing the light-emitting device may allow for subpixel arrangementsto be provided that are sufficiently small for use in a high-resolutiondisplay structure. The methods may allow for subpixel structures to beprovided that are smaller than those attainable by conventional inkjetprinting methods.

Furthermore, the light-emitting device produced in accordance with thepresent disclosure may possess one or more improved properties. Forexample, the materials and structure of the light-emitting device of thepresent disclosure may promote stability of the crosslinked matrix, evenupon exposure to ambient UV light (e.g. the emission received from thesun). As another example, the long-term stability and performance of theQDs of the light emitting device of the present disclosure may beimproved. The QDs being dispersed in an organic matrix may be protectedfrom moisture, humidity, and/or reactive oxygen species (e.g. peroxides,superoxide, hydroxyl radical, and singlet oxygen). This may reduce orprevent the device from exhibiting a change in light output during agingeither with or without electrical bias applied.

In accordance with one aspect of the present disclosure, alight-emitting device includes: an anode; a cathode; and an emissivelayer disposed between the anode and the cathode, the emissive layerincluding quantum dots dispersed in a crosslinked matrix formed from oneor more crosslinkable charge transport materials.

In some embodiments, the quantum dots form part of the crosslinkedmatrix.

In some embodiments, the quantum dots include ligands having one or morefunctional groups.

In some embodiments, the one or more crosslinkable charge transportmaterial includes one or more hole transport materials.

In some embodiments, the one or more crosslinkable charge transportmaterial includes one or more electron transport materials.

In some embodiments, the light-emitting device further includes a holetransport layer disposed between the anode and the emissive layer. Thehole transport layer may be crosslinked with the matrix of the emissivelayer. The light-emitting device may further include a hole injectionlayer disposed between the anode and the hole transport layer.

In some embodiments, the light-emitting device further includes anelectron transport layer disposed between the cathode and the emissivelayer. The electron transport layer may be crosslinked with the matrixof the emissive layer.

In some embodiments, the emissive layer further includes one or morephoto initiators.

In accordance with another aspect of the present disclosure, a pixel ofa display includes an arrangement of subpixels, at least one of thesubpixels including an instance of the light-emitting device of thepresent disclosure. The subpixels may be respectively configured suchthat they produce different respective colors.

In accordance with another aspect of the present disclosure, a method offorming an emissive layer of a light-emitting device includes:depositing a mixture including quantum dots and one or morecrosslinkable charge transport materials on a layer; and subjecting atleast a portion of the mixture to UV activation to form an emissivelayer including quantum dots dispersed in a crosslinked matrix.

In some embodiments, the quantum dots form part of the crosslinkedmatrix.

In some embodiments, the quantum dots include ligands at their outersurface.

In some embodiments, the mixture further including a photo initiator.

In some embodiments, the layer is an electrode.

In some embodiments, the layer is a hole transport layer.

In some embodiments, the hole transport layer includes a crosslinkablehole transport material, and the UV activation crosslinks the holetransport layer with the matrix of emissive layer.

In some embodiments, the layer is an electron transport layer. Theelectron transport layer may include a crosslinkable electron transportmaterial, and the UV activation may crosslink the electron transportlayer with the matrix of emissive layer.

In accordance with another aspect of the present disclosure, alight-emitting device includes: an anode; a cathode; and an emissivelayer disposed between the anode and the cathode, the emissive layerincluding quantum dots dispersed in a crosslinked matrix formed from oneor more crosslinkable charge transport materials, the one or morecrosslinkable charge transport materials including an ambipolarmaterial.

In some embodiments, the quantum dots form part of the crosslinkedmatrix.

In some embodiments, the quantum dots include ligands having one or morefunctional groups.

In some embodiments, the one or more crosslinkable charge transportmaterial further includes one or more hole transport materials.

In some embodiments, the one or more crosslinkable charge transportmaterial further includes one or more electron transport materials.

In some embodiments, the light-emitting device further includes a holetransport layer disposed between the anode and the emissive layer.

In some embodiments, the hole transport layer is crosslinked with thematrix of the emissive layer.

In some embodiments, the light-emitting device further includes a holeinjection layer disposed between the anode and the hole transport layer.

In some embodiments, the light-emitting device further includes anelectron transport layer disposed between the cathode and the emissivelayer.

In some embodiments, the electron transport layer is crosslinked withthe matrix of the emissive layer.

In some embodiments, the light-emitting device further includes anelectron injection layer disposed between the cathode and the electrontransport layer.

In some embodiments, the emissive layer further includes one or morephoto initiators.

In accordance with another aspect of the present disclosure a method offorming an emissive layer of a light-emitting device includes:depositing a mixture including quantum dots and one or morecrosslinkable charge transport materials on a layer, the one or morecrosslinkable charge transport materials including an ambipolarmaterial; and subjecting at least a portion of the mixture to UVactivation to form an emissive layer including quantum dots dispersed ina crosslinked matrix.

In some embodiments, the quantum dots form part of the crosslinkedmatrix.

In some embodiments, the quantum dots include ligands at their outersurface.

In some embodiments, the mixture further includes a photo initiator.

In some embodiments, the layer is an electrode.

In some embodiments, the layer is an ambipolar transport layer.

In some embodiments, the layer is a hole transport layer.

In some embodiments, the hole transport layer includes a crosslinkablehole transport material, and the UV activation crosslinks the holetransport layer with the matrix of emissive layer.

In some embodiments, the layer is an electron transport layer.

In some embodiments, the electron transport layer includes acrosslinkable electron transport material, and the UV activationcrosslinks the electron transport layer with the matrix of emissivelayer.

The foregoing and other features of the invention are hereinafterdescribed in greater detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of an exemplarylight-emitting device in accordance with the present disclosure.

FIGS. 2 and 3 are schematic cross-sectional views of exemplarycrosslinked emissive layers in accordance with the present disclosure.

FIGS. 4-6 are schematic cross-sectional views of exemplarylight-emitting devices in accordance with the present disclosure.

FIGS. 7 and 8 are schematic cross-sectional views of parts ofcrosslinked emissive layers in accordance with the present disclosurecrosslinked together with an adjacent charge transport layer.

FIGS. 9 and 10 are schematic cross-sectional views of parts ofcrosslinked emissive layers in accordance with the present disclosurecrosslinked together with adjacent charge transport layers.

FIG. 11 is an energy diagram of an exemplary embodiment of alight-emitting device produced in accordance with the presentdisclosure.

FIG. 12 is an energy diagram of an exemplary embodiment of alight-emitting device produced in accordance with the presentdisclosure.

FIGS. 13A-13E are schematic cross-sectional views showing production ofparts of an exemplary light-emitting device produced in accordance withan exemplary method of the present disclosure.

FIGS. 14A-14E are schematic cross-sectional views showing production ofparts of an exemplary light-emitting device produced in accordance withan exemplary method of the present disclosure.

FIG. 15A is a schematic cross-sectional view of two patterned subpixelsin accordance with an exemplary embodiment of the present disclosure.

FIG. 15B is a schematic top view of the exemplary embodiment of FIG. 15Awithout the common cathode shown.

DESCRIPTION

Referring now to the drawings in detail and initially to FIG. 1, anexemplary light-emitting device is indicated generally by referencenumeral 100. As shown, a stack of layers is provided on a substrate 102.The layers include electrodes 104, 106 and an emissive layer 108disposed between the electrodes. In some embodiments, such as the oneshown, the stack is formed such that the anode is proximate thesubstrate. Accordingly, in the illustrated embodiment, the order of thelayers moving away from the substrate is an anode 104, emissive layer108, and cathode 106. Although not specifically shown, in otherembodiments, the layers may be stacked on the substrate in reverse ordersuch that the cathode is proximate the substrate. During operation, abias may be applied between the anode 104 and the cathode 106. Thecathode 106 injects electrons into the emissive layer 108. Likewise, theanode 104 injects holes into the emissive layer. The electrons and holesradiatively recombine and light is emitted.

The substrate 102 may be made from any suitable material(s). Exemplarysubstrates include glass substrates and polymer substrates. Morespecific examples of substrate material(s) include polyim ides,polyethenes, polyethylenes, polyesters, polycarbonates,polyethersulfones, polypropylenes, and/or polyether ether ketones. Thesubstrate 102 may be any suitable shape and size. In some embodiments,the dimensions of the substrate allow for more than one light-emittingdevice to be provided thereon. In an example, a major surface of thesubstrate may provide an area for multiple light-emitting devices to beformed as sub-pixels of a pixel. In another example, a major surface ofthe substrate may provide an area for multiple pixels to be formedthereon, each pixel including a sub-pixel arrangement of light-emittingdevices.

The electrodes 104, 106 may be made from any suitable material(s). Insome embodiments, at least one of the electrodes is a transparent orsemi-transparent electrode. In some embodiments, at least one of theelectrodes is a reflective electrode. In some embodiments, one of theelectrodes is a transparent or semi-transparent electrode and the otherelectrode is a reflective electrode. Exemplary electrode materialsinclude one or more metals (e.g., aluminum, gold, silver, platinum,magnesium and the like and alloys thereof) or metal oxides (e.g., indiumtin oxide, indium-doped zinc oxide (IZO), fluorine doped tin oxide(FTO), aluminum-doped zinc-oxide (AZO), indium-doped cadmium-oxide, andthe like). The electrodes 104, 106 may also be provided in any suitablearrangement. As an example, the electrodes 104, 106 may address athin-film transistor (TFT) circuit.

The emissive layer 108 may include a crosslinked matrix of one or morecrosslinked charge transport materials in which quantum dots (QDs) aredispersed. Exemplary matrix structures are schematically shown in FIGS.2 and 3. In some embodiments, and with additional reference to FIG. 2,the crosslinked charge transport material 202 may form a conductiveinsoluble matrix that disperses the QDs 204. The term “insoluble”, asused herein in connection with “insoluble matrix”, is indicative of thematrix being insoluble in the solvent in which the QDs and the chargetransport materials are initially dispersed during formation of theemissive layer, or in a solvent having similar properties to those usedto disperse the QDs and the transporting materials. Such similarsolvents may have one or more similar properties such as polarity(dielectric constant), protic-aprotic property, and the like. Thesimilar solvent may be an “orthogonal solvent” in that it is does notdissolve the matrix deposited from the other solvent. As such, theconductive insoluble matrix may be insoluble in orthogonal solvents.

As shown in FIG. 2, the charge transport materials are joined at bondlocations 206 to form the matrix, and the QDs 204 are dispersed andretained within the cross-linked matrix. In other embodiments, and withadditional reference to FIG. 3, the crosslinked charge transportmaterial 202 may form the conductive insoluble matrix together with theQDs 204. As shown, the charge transport materials are joined atrespective bond locations 206 to form the matrix, and the QDs 204 arealso joined at respective bond locations 206 to the charge transportmaterial 202. As such, the QDs 204 form a part of the matrix network. Insome embodiments, the one or more charge transport materials may beUV-induced crosslinked charge transport materials.

Exemplary QDs 204 include one or more of: InP, CdSe, CdS,CdSe_(x)S_(1-x), CdTe, Cd_(x)Zn_(1-x)Se, Cd_(x)Zn_(1-x)Se_(y)S_(1-y),ZnSe, ZnS, ZnS_(x)Te_(1-x), ZnSe_(x)Te_(1-x), perovskites of the formABX₃, Zn_(w)Cu_(z)In_(1−(w+z))S, and carbon, where θ≤w, x, y, z≤1 and(w+z)≤1. The QDs 204 may be embodied as nanoparticles. In someembodiments, the QDs 204 include ligands 208. The ligands may beprovided on the outer surface of the QDs. As an example, the quantumdots may include a core, a shell around the core, and ligands around theshell. In other embodiments, the quantum dots may include a core, ashell around the core, an oxide layer (e.g. an Al₂O₃ layer or a layer ofanother suitable metal oxide), and ligands around the oxide layer. Insome examples, the ligand 208 may be an organic material that makes theQDs 204 dispersible in the crosslinkable charge transport material thatis used in forming the emissive layer 108. In some examples, the ligandsinclude a functional group that may interact with the crosslinkablecharge transport material (e.g., via external stimuli such astemperature, pressure, and/or radiation) in forming the emissive layer(e.g., in the manner shown in FIG. 3). Exemplary functional groups ofthe ligands may include thiols, alkenes, alkynes, carbonyl and/orcarboxyl functional groups. As shown in FIG. 2, while the QDs mayinclude ligands, they may not interact with the charge transportmaterial in forming the matrix. But as shown in FIG. 3, the ligands andcharge transport material may be selected such that the ligand doesinteract with the charge transport material to incorporate the QDs aspart of the formed matrix. Of course, in other embodiments, the QDs maynot include ligands.

In some embodiments, the QDs 204 are present in the emissive layer in anamount from 0.01 wt % to 85 wt %. In other embodiments, the QDs 204 arepresent in the emissive layer in an amount from 0.01 wt % to 60 wt %. Inother embodiments, the QDs 204 are present in the emissive layer in anamount from 0.01 wt % to 40 wt %.

Exemplary UV-induced crosslinked charge transport materials 202 includeUV-induced crosslinked hole transport materials and/or UV-inducedcrosslinked electron transport materials and/or UV-induced crosslinkedambipolar transport materials. Accordingly, the matrix of one or moreUV-induced crosslinked charge transport materials may be formed from oneor more types of crosslinkable materials. Such materials include one ormore hole transport materials and/or one or more electron transportmaterials and/or one or more ambipolar materials. An ambipolar materialis a material that has both hole and electron transporting properties.In some embodiments, the crosslinkable hole transport material may be amaterial which is an effective hole transporter both without and withcrosslinking. In other embodiments, the crosslinkable hole transportmaterial may be a material which is an effective hole transporter onlywhen crosslinked. In some embodiments, the crosslinkable electrontransport material may be a material which is an effective electrontransporter both without and with crosslinking. In other embodiments,the crosslinkable electron transport material may be a material which isan effective electron transporter only when crosslinked. In someembodiments, the crosslinkable ambipolar transport material may be amaterial which is an effective ambipolar transporter both without andwith crosslinking. In other embodiments, the crosslinkable ambipolartransport material may be a material which is an effective ambipolartransporter only when crosslinked. In some embodiments, the crosslinkedcharge transport materials 202 can include one or more of hole injectionmaterials, electron injection materials, hole blocking materials,electron blocking materials, ambipolar materials, and/or interconnectingmaterials (ICM).

Using a cross-linkable ambipolar material that disperses QDs in theemissive layer 108 can help to simplify the QD-LED structure. Using suchmaterial, the hole transport layer and electron transport layer can beexcluded from the structure (e.g., as exemplified in the structure shownin FIG. 1) because the ambipolar material can efficiently transport bothholes and electrons. This means that the fabrication of a QD-LED caninvolve the deposition of less layers making the fabrication an easier,faster and simpler process. Dispersing QDs in a cross-linkable ambipolarmaterial encourages transfer of both carriers in the emissive layer, andtherefore helps get emission from throughout the height of the emissivelayer, rather than just at the top or bottom of the emissive layer asfor a conventional QLED. This can help to suppress cavity effects thatcause the intensity to vary with direction. However, while theabove-mentioned examples discuss the use of ambipolar material in theemissive layer it will be appreciated that in some embodiments, theemissive layer of structure shown in FIG. 1 may include one or more holetransport materials; or may include one or more electron transportmaterials; or may include one or more hole transport materials and oneor more electron transport materials; or may include one or more holetransport materials and/or one or more electron transport materialsand/or one or more ambipolar materials. In such embodiments, an electrontransport layer and a hole transport layer may not be included.

In some embodiments, the crosslinkable material from which theUV-induced crosslinked charge transport material (e.g., the one or morehole transport materials and/or one or more electron transport materialsand/or one or more ambipolar materials) may be formed includes at leasttwo moieties with different characteristics. As an example, one of theat least two moieties of the molecule may provide charge transportingproperties and another of the at least two moieties of the molecule mayprovide UV-cross-linking capabilities. As another example, two of the atleast two moieties of the molecule may provide charge transportingproperties. In the exemplary case of an ambipolar material, one of theat least two moieties of the molecule may provide hole transportingproperties and another of the at least two moieties of the molecule mayprovide electron transporting properties. In another exemplary case of ahole transport material, two of the at least two moieties of themolecule may provide hole transporting properties. In another exemplarycase of an electron transport material, two of the at least two moietiesof the molecule may provide electron transporting properties. As anotherexample, two of the moieties of the molecule may provide chargetransporting properties and another one of the moieties of the moleculemay provide UV-cross-linking capabilities. Exemplary moieties that mayprovide charge transporting properties include, but are not limited to,tertiary, secondary, and primary aromatic or aliphatic amines, tryarylphosphines, and quinolinolates. Exemplary moieties that may provideUV-cross-linking capabilities include, but are not limited to, oxetane,epoxy, thiol, alkene, alkyne, ketone, and aldehyde units. In someimplementations, the two moieties may be connected and between themthere may be a distance of less than 20 nm.

One example of a crosslinkable material from which the UV-inducedcrosslinked hole transport material may be formed isN4,N4′-Bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyl)phenyl)-N4,N4′-diphenylbiphenyl-4,4′-diamine(OTPD), shown below in Formula 1. In some embodiments, the crosslinkablematerial shown in Formula 1 may be used in forming the matrix shown inFIG. 2.

Another example of a crosslinkable material from which the UV-inducedcrosslinked hole transport material may be formed isN4,N4′-Bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyloxy)phenyl)-N4,N4′-bis(4-methoxyphenyl)biphenyl-4,4′-diamine(QUPD), shown below in Formula 2. In some embodiments, the crosslinkablematerial shown in Formula 2 may be used in forming the matrix shown inFIG. 2.

Another example of a crosslinkable material from which the UV-inducedcrosslinked hole transport material may be formed isN,N′-(4,4′-(Cyclohexane-1,1-diyl)bis(4,1-phenylene))bis(N-(4-(6-(2-ethyloxetan-2-yloxy)hexyl)phenyl)-3,4,5-trifluoroaniline)(X-F6-TAPC), shown below in Formula 3. In some embodiments, thecrosslinkable material shown in Formula 3 may be used in forming thematrix shown in FIG. 2.

An example of a crosslinkable material from which the UV-inducedcrosslinked electron transport material may be formed isN4,N4′-Di(naphthalen-1-yl)-N4,N4′-bis(4-vinylphenyl)biphenyl-4,4′-diamine(VNPB), shown below in Formula 4. In some embodiments, the crosslinkablematerial shown in Formula 4 may be used in forming the matrix shown inFIG. 3.

Another example of a crosslinkable material from which the UV-inducedcrosslinked electron transport material may be formed is9,9-Bis[4-[(4-ethenylphenyl)methoxy]phenyl]-N2,N7-di-1-naphthalenyl-N2,N7-diphenyl-9H-Fluorene-2,7-diamine(VB-FNPD), shown below in Formula 5. In some embodiments, thecrosslinkable material shown in Formula 5 may be used in forming thematrix shown in FIG. 3.

In some embodiments the emissive layer is formed using one or more photoinitiators. As such, the emissive layer may include one or more photoinitiators. A photo initiator is a material that initiatespolymerizations by a light stimuli. In some embodiments, the photoinitiator may generate one or more radicals, ions, acids, and/or speciesthat may initiate such polymerization. Examples include, but are notlimited to, cationic species and/or radicals, BrOnsted acids, carbeniumions, or onium ions by light irradiation. Exemplary photo initiatorsinclude sulfonium- and iodonium-salts (e.g. triphenylsulfonium triflateand diphenyliodonium triflate).

In the embodiments described above, the light-emitting device includeselectrodes 104, 106 and an emissive layer 108 disposed between theelectrodes. In other embodiments, the light-emitting device may includeone or more additional layers. These one or more additional layers mayinclude one or more transport layers (e.g., hole transport layer,electron transport layer) and/or one or more injection layers (e.g.,hole injection layer, electron injection layer).

FIG. 4 shows another exemplary embodiment of a light-emitting device200. The light-emitting device is similar to the light-emitting device100 described above, but it additionally includes an electron transportlayer 110. As shown, a stack of layers is provided on a substrate 102.The layers include electrodes 104, 106, an emissive layer 108, and anelectron transport layer 110. Both the emissive layer 108 and theelectron transport layer 110 are disposed between the electrodes, withthe emissive layer 108 proximate the anode 104 and the electrontransport layer 110 proximate the cathode 106. In some embodiments, suchas the one shown, the stack is formed such that the anode is proximatethe substrate. Although not specifically shown, in other embodiments,the layers may be stacked on the substrate in reverse order such thatthe cathode is proximate the substrate. During operation, a bias may beapplied between the anode 104 and the cathode 106. The structure mayprovide for recombination of holes and electrons in a portion of theemission layer 108 proximate the interface of the emission layer 108 andthe electron transport layer 110.

The electrodes 104, 106 and the emissive layer 108 may be embodied asany of the embodiments described above (e.g., in connection with FIG.1). In some embodiments, the emissive layer 108 may be configured suchthat the UV-induced crosslinked charge transport material includes oneor more UV-induced crosslinked hole transport materials.

The electron transport layer 110 may include one or more layersconfigured to transport electrons therethrough from the cathode to theemissive layer. The electron transport layer 110 may be made from anysuitable material(s). In some embodiments, the electron transport layer110 may include one or more of ZnO, 8-quinolinolato lithium (Liq.), LiF,Cs₂CO₃, Mg_(x)Zn_(1-x)O where 0≤x≤1, Al_(x)Zn_(1-x)O where0≤x≤1,2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)(TPBi), TiO₂, ZrO₂,N4,N4′-Di(naphthalen-1-yl)-N4,N4′-bis(4-vinylphenyl)biphenyl-4,4′-diamine(VNPB), and9,9-Bis[4-[(4-ethenylphenyl)methoxy]phenyl]-N2,N7-di-1-naphthalenyl-N2,N7-diphenyl-9H-Fluorene-2,7-diamine(VB-FNPD). In embodiments where the electron transport layer 110includes more than one layer, the material of one of the respectivelayers may differ from the material of one or more of the otherlayers(s).

In some embodiments, the electron transport layer 110 and the emissivelayer 108 include the same electron transport material. In otherembodiments, the electron transport layer 110 and the emissive layer 108include different respective materials.

In some embodiments, the electron transport layer does not include acrosslinkable transport material. In other embodiments, the electrontransport material includes one or more crosslinkable transportmaterials. In embodiments where the electron transport material includesone or more crosslinkable transport materials, the crosslinked matrixwithin the emissive layer may be crosslinked to (and extend into) theelectron transport layer. This crosslinking is exemplified in FIGS. 7and 8.

FIG. 5 shows another exemplary embodiment of a light-emitting device300. The light-emitting device 300 is similar to the light-emittingdevice 100 described above, but it additionally includes a holetransport layer 112. As shown, a stack of layers is provided on asubstrate 102. The layers include electrodes 104, 106, an emissive layer108, and a hole transport layer 112. Both the emissive layer 108 and thehole transport layer 112 are disposed between the electrodes, with theemissive layer 108 proximate the cathode 106 and the hole transportlayer 112 proximate the anode 104. In some embodiments, such as the oneshown, the stack is formed such that the anode is proximate thesubstrate. Although not specifically shown, in other embodiments, thelayers may be stacked on the substrate in reverse order such that thecathode is proximate the substrate. During operation, a bias may beapplied between the anode 104 and the cathode 106. The structure mayprovide for recombination of holes and electrons in a portion of theemission layer 108 proximate the interface of the emission layer 108 andthe hole transport layer 112.

The electrodes 104, 106 and the emissive layer 108 may be embodied asany of the embodiments described above (e.g., in connection with FIG.1). In some embodiments, the emissive layer 108 may be configured suchthat the UV-induced crosslinked charge transport material includes oneor more UV-induced crosslinked electron transport materials.

The hole transport layer 112 may include one or more layers configuredto transport holes therethrough from the anode to the emissive layer.The hole transport layer 106 may be made from any suitable material(s).In some embodiments, the hole transport layer 112 may include one ormore of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)(PEDOT:PSS),poly(9,9-dioctylfluorene-co-N-(4-sec-butylphenyl)-diphenylamine) (TFB),poly(9-vinylcarbazole) (PVK), poly(N, N′-bis(4-butylphenyl)-N,N′-bisphenylbenzidine) (PolyTPD), V₂O₅, NiO, CuO, WO₃, MoO₃,2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ),1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HATCN),N4,N4′-Bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyl)phenyl)-N4,N4′-diphenylbiphenyl-4,4′-diamine(OTPD),N4,N4′-Bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyloxy)phenyl)-N4,N4′-bis(4-methoxyphenyl)biphenyl-4,4′-diamine(QUPD), andN,N′-(4,4′-(Cyclohexane-1,1-diyl)bis(4,1-phenylene))bis(N-(4-(6-(2-ethyloxetan-2-yloxy)hexyl)phenyl)-3,4,5-trifluoroaniline)(X-F6-TAPC). In embodiments where the hole transport layer 112 includesmore than one layer, the material of one of the respective layers maydiffer from the material of one or more of the other layers(s).

In some embodiments, the hole transport layer 112 and the emissive layer108 include the same hole transport material. In other embodiments, thehole transport layer 112 and the emissive layer 108 include differentrespective materials.

In some embodiments, the hole transport layer does not include acrosslinkable transport material. In other embodiments, the holetransport material includes one or more crosslinkable transportmaterials. In embodiments where the hole transport material includes oneor more crosslinkable transport materials, the crosslinked matrix withinthe emissive layer may be crosslinked to (and extend into) the holetransport layer. This crosslinking is exemplified in FIGS. 7 and 8.

FIG. 6 shows another exemplary embodiment of a light-emitting device400. The light-emitting device 400 is similar to the light-emittingdevice 100 described above, but it additionally includes a holetransport layer 112 and an electron transport layer 110. As shown, astack of layers is provided on a substrate 102. The layers includeelectrodes 104, 106; charge transport layers 110, 112; and an emissivelayer 108. In the exemplary embodiment shown, the charge transportlayers 110, 112 are disposed between the electrodes 104, 106 and theemissive layer 108 is disposed between the charge transport layers 110,112.

In some embodiments, such as the one shown, the stack is formed suchthat the anode is proximate the substrate. Accordingly, in theillustrated embodiment, the order of the layers moving away from thesubstrate is an anode 104, hole transport layer 112, emissive layer 108,electron transport layer 110, and cathode 106. Although not specificallyshown, in other embodiments, the layers may be stacked on the substratein reverse order such that the cathode is proximate the substrate.During operation, a bias may be applied between the anode 104 and thecathode 106. The cathode 106 injects electrons into the electrontransport layer 110 adjacent to it. Likewise, the anode 104 injectsholes into the hole transport layer 112 adjacent to it. The electronsand holes respectively propagate through the hole transport layer andthe electron transport layer to the emissive layer 108 where theyradiatively recombine and light is emitted.

The electrodes 104, 106 and the emissive layer 108 may be embodied asany of the embodiments described above (e.g., in connection with FIGS.1, 4 and 5). The electron transport layer 110 may be embodied as any ofthe embodiments described above (e.g., in connection with the embodimentof FIG. 4). In some embodiments, the electron transport layer 110 andthe emissive layer 108 include the same electron transport material. Inother embodiments, the electron transport layer 110 and the emissivelayer 108 include different respective electron transport materials. Thehole transport layer 112 may be embodied as any of the embodimentsdescribed above (e.g., in connection with the embodiment of FIG. 5). Insome embodiments, the hole transport layer 112 and the emissive layer108 include the same hole transport material. In other embodiments, thehole transport layer 112 and the emissive layer 108 include differentrespective hole transport materials.

In still other embodiments, the light-emitting device may include one ormore additional layers. Examples include a hole injection layer and/oran electron injection layer. Exemplary materials suitable for use in ahole injection layer include, but are not limited to,poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS),MoO₃:PEDOT:PSS; V₂O₅, WO₃, MoO₃,2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), and/or1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HATCN). Exemplarymaterials suitable for use in an electron injection layer include, butare not limited to, 8-quinolinolato lithium (Liq), LiF, and/or Cs₂CO₃.

As exemplified in the embodiments described in connection with FIGS.4-6, the emissive layer 108 may be adjacent a hole transport layer 112and/or an electron transport layer 110. In some embodiments, theelectron transport layer 110 and/or the hole transport layer 112 doesnot include a crosslinkable transport material. In other embodiments,the electron transport material of the electron transport layer 110and/or the hole transport material of the hole transport layer 112includes one or more crosslinkable transport materials. As such, in someembodiments, the crosslinked matrix within the emissive layer may becrosslinked to (and extend into) the electron transport layer 110 and/orthe hole transport layer 112. This is exemplified in FIGS. 7 and 8. FIG.7 shows a cross-sectional view of exemplary interactions occurring usingan additional crosslinkable material as charge transport material in theadjacent charge transport layer 110/112, where the structure of theemissive layer 108 is similar to that described in connection with FIG.2. FIG. 8 shows a cross-sectional view of exemplary interactionsoccurring using an additional crosslinkable material as charge transportmaterial in the adjacent charge transport layer 110/112, where thestructure of the emissive layer 108 is similar to that described inconnection with FIG. 3. Interactions at the interfaces between chargetransport layer and the emissive layer promote anchoring between theadjacent layers. While FIGS. 7 and 8 show the crosslinking between twoadjacent layers, although not specifically shown, in some embodiments(e.g., such as that in FIG. 6 where the emissive layer 108 is adjacentboth the electron transport layer 110 and the hole transport layer 112)the emissive layer 108 may be crosslinked with both the electrontransport layer 110 and with the hole transport layer 112. This isexemplified in FIGS. 9 and 10.

FIG. 9 shows a cross-sectional view of exemplary interactions occurringusing an additional crosslinkable material as charge transport materialin the adjacent electron transport layer 110 and hole transport layer112, where the structure of the emissive layer 108 is similar to thatdescribed in connection with FIG. 2. The crosslinked matrix within theemissive layer may be crosslinked to (and extend into) the electrontransport layer 110 and hole transport layer 112. FIG. 10 shows across-sectional view of exemplary interactions occurring using anadditional crosslinkable material as charge transport material in theadjacent electron transport layer 110 and hole transport layer 112,where the structure of the emissive layer 108 is similar to thatdescribed in connection with FIG. 3. The crosslinked matrix within theemissive layer may be crosslinked to (and extend into) the electrontransport layer 110 and hole transport layer 112. However, it will beappreciated that in embodiments of the light-emitting device such asthat shown in FIG. 6 where an electron transport layer 110 and holetransport layer 112 are adjacent to respective surfaces of the emissivelayer 108, the emissive layer 108 may be crosslinked to only one of theelectron transport layer 110 or the hole transport layer 112 (e.g., suchas that shown in FIGS. 7 and 8). That is, in some embodiments, theemissive layer 108 may be crosslinked with one of the electron transportlayer 110 or the hole transport layer 112 and not crosslinked with theother of the electron transport layer 110 or the hole transport layer112. FIG. 11 shows an energy diagram of an exemplary embodiment of alight-emitting device produced in accordance with the presentdisclosure. It is noted that the device depicted in the energy diagramincludes a hole injection layer 109 disposed between the anode 104 andthe hole transport layer 112. The diagram demonstrates that when theemissive layer includes a crosslinked hole transport material (dottedbox 108), the difference of energy between the ionization potential ofthe emissive layer 108 and of the hole transport layer 112 is decreasedas compared to when the emissive layer does not include the crosslinkedhole transport material (solid box 108). Although not shown, a similareffect may be achieved when the emissive layer includes a crosslinkedelectron transport material: the difference of energy between theelectron affinity of the emissive layer and of the electron transportlayer would be decreased as compared to when the emissive layer does notinclude the crosslinked hole transport material.

FIG. 12 shows an energy diagram of another exemplary embodiment of alight-emitting device produced in accordance with the presentdisclosure. It is noted that the device depicted in the energy diagramincludes a hole injection layer 109 disposed between the anode 104 andthe hole transport layer 112. The diagram demonstrates that when theemissive layer includes a crosslinked ambipolar material (dotted box108), the difference of energies between the ionization potential of theemissive layer 108 and of the hole transport layer 112, and between theelectron affinity of emissive layer 108 and of the electron transportinglayer 110 are decreased, as compared to when the emissive layer does notinclude the crosslinked ambipolar material (solid box 108). Turning nowto FIGS. 13A-13E, an exemplary method of producing the crosslinkedemissive layer is described. As shown in FIG. 13A, a substrate 102 isprovided. As shown in FIG. 13B, an electrode 104 is deposited on thesubstrate 102. The electrode 104 may be deposited on the substrate usingany suitable method. Examples include sputtering, evaporative coating,printing, chemical vapor deposition, and the like. As described above,the deposited electrode may be provided in any suitable form. Oneexemplary implementation is an electrode for a TFT circuit.

As shown in FIG. 13C, a mixture 107 of UV-induced crosslinkable chargetransport material 202 and QDs 204 in a solvent 205 is deposited on topof the electrode 104 and the substrate 102. In some embodiments, themixture 107 additionally includes photo initiator. The charge transportmaterial 202 may include one or more crosslinkable hole transportmaterials and/or one or more crosslinkable electron transport materials.The crosslinkable charge transport material may include at least twomoieties with different characteristics. As an example, one of the atleast two moieties of the molecule may provide charge transportingproperties and another of the at least two moieties of the molecule mayprovide UV-cross-linking capabilities. As another example, two of the atleast two moieties of the molecule may provide charge transportingproperties. In the exemplary case of an am bipolar material, one of theat least two moieties of the molecule may provide hole transportingproperties and another of the at least two moieties of the molecule mayprovide electron transporting properties. In another exemplary case of ahole transport material, two of the at least two moieties of themolecule may provide hole transporting properties. In another exemplarycase of an electron transport material, two of the at least two moietiesof the molecule may provide electron transporting properties. As anotherexample, two of the moieties of the molecule may provide chargetransporting properties and another one of the moieties of the moleculemay provide UV-cross-linking capabilities. In some embodiments, the QDs204 include ligands. Exemplary hole transport materials and/or one ormore charge transport materials and QDs are described above. In someembodiments, the UV-induced crosslinkable charge transport material mayinclude one or more of the structure shown above in Formulas 1-3.

The solvent 205 may be any suitable solvent. In some embodiments, thesolvent 205 is selected such that the QDs and crosslinkable chargetransport materials (and photo initiator, if included) are solubletherein. Exemplary solvents include, but are not limited to thefollowing or mixtures including the following: acetone, dichloromethane,chloroform, linear or branched alkyl acetates (e.g. ethyl acetate,n-butyl acetate, 2-butyl acetate), linear or branched alkanes with 3 to30 atoms of carbon (e.g., pentane, hexane, heptane, octane, nonane,decane, undecane, dodecane), linear or branched alcohols with 1 to 10atoms of carbon (e.g., butanol, 2-propanol, propanol, ethanol,methanol), linear or branched alkoxy alcohols with 2 to 10 atoms ofcarbon (e.g., 2-Methoxyethanol, 2-Ethoxyethanol), mono, di and trihalogen substituted benzenes (e.g., chlorobenzene, 1,2-dibromobenzene,1,3-dibromobenzene, 1,4-dibromobenzene, 1,3,5-tribromobenzene,1,2,4-tribromobenzene), linear or branched ethers with 2 to 20 atoms ofcarbon, and/or mono, di and tri alkyl substituted benzenes (e.g.,toluene, 1,2-Dimethylbenzene, 1,3-Dimethylbenzene, 1,4-Dimethylbenzene),benzene, dioxane, propylene glycol monomethyl ether acetate (PGMEA). Theparticular solvent that is utilized may depend on the specific chargetransporting material, QDs, and photo initiator that are selected.

As shown in FIG. 13D, UV light 302 is applied though a mask 304 thatprovides a shape/pattern through which the desired area of the mixture107 is exposed. Exposure of the mixture 107 to UV light results in thecross-linking of the charge transport material. In embodiments where themixture includes photo initiator, the photo initiator may assist ininitializing the cross-linking of the charge transport material. Thecross-linking of the charge transport material results in dispersion ofthe QDs throughout the formed crosslinked matrix of the charge transportmaterial. The crosslinked mixture forms the emissive layer 108, which isinsoluble. The remaining mixture may be washed away with a solvent. Insome embodiments, the solvent is the same solvent used in the mixture107 that is deposited in FIG. 13C. In other embodiments, the solvent isa similar solvent or orthogonal solvent to the solvent used in themixture 107 that is deposited in FIG. 13C. Accordingly, as shown in FIG.10E, the crosslinked emissive layer 108 remains on the electrode 102. Asshown, the QDs 204 are dispersed in the solid matrix formed bycrosslinking the charge transport material 202.

The solvent used in the mixture 107 and/or the solvent used to wash awaythe remaining mixture may be evaporated during curing (e.g., heating) ofthe deposited layer. The curing may be performed at any suitabletemperature that effectuates evaporation of the solvent while alsomaintaining the integrity of the QDs and charge transport material. Insome embodiments, curing may be performed at a temperature ranging from5° C. to 150° C. In other embodiments, curing may be performed at atemperature ranging from 30° C. to 150° C. In other embodiments, curingmay be performed at a temperature ranging from 30° C. to 100° C.

As an example, subsequent to the application of UV light (as shown inFIG. 13D), the layer may be cured (e.g., heated) to facilitateevaporation/removal of the solvent(s). This curing may be performedprior to the washing or subsequent to the washing. In thoseimplementations where the curing is performed prior to the washing, asubsequent curing may be performed after washing. As another example,application of UV light (as shown in FIG. 13D) and curing (e.g.,heating) may be performed in parallel. This may remove the solvent usedin the mixture 107. Subsequent to the washing, a subsequent curing maybe performed. As yet another example, curing may be conducted priorapplication of UV light (as shown in FIG. 13D). Subsequent to thewashing, a subsequent curing may be performed.

Factors such as the UV exposure times, UV-intensity, amount of photoinitiator and ratio between UV-reactive moieties may allow for controlof the morphology of the emissive material. For example, UV exposuretime may in some embodiments range from 0.1 second to 15 minutes. UVexposure intensity may range from 0.1 to 100,000 mJ/cm². The amount ofphoto initiator may range from 0.001 to 10 wt % of the mixture. Theratio between UV reactive moieties may range from 0.001 to 1. In oneexemplary implementation, the UV exposure intensity ranges from 1 to 100mJ/cm² at a UV exposure time of 1 to 10 seconds.

Turning now to FIGS. 14A-14E, another exemplary method of producing thecrosslinked emissive layer is described. The method described inconnection with FIGS. 14A-14E is similar to the method described inconnection with FIGS. 13A-13E, but the mixture 107 from which theemissive layer is formed includes a combination of QDs having ligandsand charge transport material that may interact to form the matrix withthe QDs integrated therein.

As shown in FIG. 14A, a substrate is provided. As shown in FIG. 14B, anelectrode 104 is deposited on the substrate 102. The electrode 104 maybe deposited on the substrate using any suitable method. Examplesinclude sputtering, evaporative coating, printing, chemical vapordeposition, and the like. As described above, the deposited electrodemay be provided in any suitable form. One exemplary implementation is anelectrode for a TFT circuit.

As shown in FIG. 14C, a mixture 107 of UV-induced crosslinkable chargetransport material 202 and QDs 204 in a solvent 205 is deposited on topof the electrode 104 and the substrate 102. The crosslinkable chargetransport material 202 may include at least two moieties with differentcharacteristics. As an example, one of the at least two moieties of themolecule may provide charge transporting properties and another of theat least two moieties of the molecule may provide UV-cross-linkingcapabilities. As another example, two of the at least two moieties ofthe molecule may provide charge transporting properties. In theexemplary case of an am bipolar material, one of the at least twomoieties of the molecule may provide hole transporting properties andanother of the at least two moieties of the molecule may provideelectron transporting properties. In another exemplary case of a holetransport material, two of the at least two moieties of the molecule mayprovide hole transporting properties. In another exemplary case of anelectron transport material, two of the at least two moieties of themolecule may provide electron transporting properties. As anotherexample, two of the moieties of the molecule may provide chargetransporting properties and another one of the moieties of the moleculemay provide UV-cross-linking capabilities. Furthermore, the QDs 204include crosslinkable ligands. The ligands may contain a functionalgroup X that may interact with a functional group Y of the UV-inducedcrosslinkable charge transport material. The UV-induced crosslinkablecharge transport material may include such functional group Y at two ormore molecular sites. For example, the functional group X may be at theend of the ligand; the functional groups Y may be at two ends of thehole transport and/or electron transport materials. In oneimplementation, the functional groups X may be a thiol, and the functiongroups Y may be an alkene or alkyne, or vice versa. Exemplary UV-inducedcrosslinkable charge transport material including such functional groupsare shown above in Formulas 4 and 5.

Ligands of the QDs and charge transporting materials included in theemissive layer can be selected in order to create uniform dispersion inthe deposition solvent. Materials with similar polarity indexes can beselected in order to ensure homogeneity of the deposited mixtures.

The solvent may be any suitable solvent. In some embodiments, thesolvent is selected such that the QDs and crosslinkable charge transportmaterials (and photo initiator, if included) are soluble therein.Exemplary solvents include, but are not limited to the following ormixtures including the following: acetone, dichloromethane, chloroform,linear or branched alkyl acetates (e.g. ethyl acetate, n-butyl acetate,2-butyl acetate), linear or branched alkanes with 3 to 30 atoms ofcarbon (e.g., pentane, hexane, heptane, octane, nonane, decane,undecane, dodecane), linear or branched alcohols with 1 to 10 atoms ofcarbon (e.g., butanol, 2-propanol, propanol, ethanol, methanol), linearor branched alkoxy alcohols with 2 to 10 atoms of carbon (e.g.,2-Methoxyethanol, 2-Ethoxyethanol), mono, di and tri halogen substitutedbenzenes (e.g., chlorobenzene, 1,2-dibromobenzene, 1,3-dibromobenzene,1,4-dibromobenzene, 1,3,5-tribromobenzene, 1,2,4-tribromobenzene),linear or branched ethers with 2 to 20 atoms of carbon, and/or mono, diand tri alkyl substituted benzenes (e.g., toluene, 1,2-Dimethylbenzene,1,3-Dimethylbenzene, 1,4-Dimethylbenzene), benzene, dioxane, propyleneglycol monomethyl ether acetate (PGMEA). The particular solvent that isutilized may depend on the specific charge transporting material, QDs,and photo initiator that are selected.

As shown in FIG. 14D, UV light 302 is applied though a mask 304 thatprovides a shape/pattern through which the desired area of the mixture107 is exposed. Exposure of the mixture 107 to UV light results in thecrosslinking of the charge transport material together, and in thecrosslinking of the charge transport material together with the QDs (viathe ligands). In embodiments where the mixture includes photo initiator,the photo initiator may assist in initializing the cross-linking of thecharge transport material and QDs. The cross-linking results in the QDsbeing incorporated into the solid matrix, and thereby dispersed in theemissive layer. The crosslinked mixture is insoluble, and the remainingmixture may be washed away with a solvent. In some embodiments, thesolvent is the same solvent used in the mixture 107 that is deposited inFIG. 14C. In other embodiments, the solvent is a similar solvent ororthogonal solvent to the solvent used in the mixture 107 that isdeposited in FIG. 14C. Accordingly, as shown in FIG. 11E, thecrosslinked emissive layer 108 remains on the electrode 102. As shown,the QDs form the solid matrix together with the charge transportmaterial, and are thereby dispersed therein.

The solvent used in the mixture 107 and/or the solvent used to wash awaythe remaining mixture may be evaporated during curing (e.g., heating) ofthe deposited layer. The curing may be performed at any suitabletemperature that effectuates evaporation of the solvent while alsomaintaining the integrity of the QDs and charge transport material. Insome embodiments, curing may be performed at a temperature ranging from5° C. to 150° C. In other embodiments, curing may be performed at atemperature ranging from 30° C. to 150° C. In other embodiments, curingmay be performed at a temperature ranging from 30° C. to 100° C.

As an example, subsequent to the application of UV light (as shown inFIG. 14D), the layer may be cured (e.g., heated) to facilitateevaporation/removal of the solvent(s). This curing may be performedprior to the washing or subsequent to the washing. In thoseimplementations where the curing is performed prior to the washing, asubsequent curing may be performed after washing. As another example,application of UV light (as shown in FIG. 14D) and curing (e.g.,heating) may be performed in parallel. This may remove the solvent usedin the mixture 107. Subsequent to the washing, a subsequent curing maybe performed. As yet another example, curing may be conducted priorapplication of UV light (as shown in FIG. 14D). Subsequent to thewashing, a subsequent curing may be performed.

Factors such as the UV exposure times, UV-intensity, amount of photoinitiator and ratio between UV-reactive moieties may allow for controlof the morphology of the emissive material. For example, UV exposuretime may in some embodiments range from 0.1 second to 15 minutes. UVexposure intensity may range from 0.1 to 100,000 mJ/cm². The amount ofphoto initiator may range from 0.001 to 10 wt % of the mixture. Theratio between UV reactive moieties may range fom 0.001 to 1. In oneexemplary implementation, the UV exposure intensity ranges from 1 to 100mJ/cm² at a UV exposure time of 1 to 10 seconds.

It is noted that while the examples described in connection with FIGS.13A-13E and 14A-14E indicate “UV irradiation” and “UV-inducedcross-linkable”, in some embodiments, it is possible to use other formsof radiation, such as electromagnetic radiation with wavelengths otherthan in the UV spectral range.

As a further step in either of the above-described methods, anadditional electrode may be formed on the upper surface of the emissivelayer 108. The electrode may be formed by a method such as, but notlimited to, sputtering, printing, chemical vapor deposition, and thelike. As such, the structure may form a light-emitting device have thestructure shown in FIG. 1 having an anode, emissive layer, and cathode.

The above-described methods shown in FIGS. 13A-13E and 14A-14E describethe formation of the emissive layer on the electrode. It will beunderstood that the methods are illustrative of the formation of theemissive layer, and that such methods can be implemented on layers otherthan the electrode. For example, the emissive layer may be formed inaccordance with the methods shown in FIGS. 13A-13E and 14A-14E on acharge transport layer. The charge transport layer may be deposited(e.g., coated) and cured (e.g., heated) prior to deposition of theemissive layer. In some embodiments, the charge transport layer on whichthe emissive layer is formed may include crosslinkable charge transportmaterial. Functional groups X or Y may be at one or more sites in themolecule (e.g. at one or more ends of the molecule). When UV irradiationis applied, the molecules of charge transport layer(s) can createinteractions at the interface with the emissive layer. This structure isexemplified in FIGS. 7-10. With reference to FIG. 7, in the methoddescribed in connection with FIGS. 13A-13E, the charge transportmaterial of the charge transport layer(s) can interact with theUV-induced crosslinkable material included in the mixture that forms theemissive layer, thereby extending the conductive insoluble matrixstructure into the charge transport layer. With reference to FIG. 8, inthe method described in connection with FIGS. 14A-14E, the chargetransport material of the charge transport layer(s) can interact withthe ligands of the QDs and/or with the UV-induced crosslinkablematerial, thereby extending the conductive insoluble matrix structureinto the charge transport layer.

Furthermore, in some embodiments, in either of the above-describedmethods, one or more additional layers (e.g., charge transport layer(s)such as hole transport layer and/or electron transport layer) may beformed below (underneath) and/or above (on top) of the emissive layer108. These layers may be formed via deposition (e.g., coating) andcuring (e.g., heating). As such, the structure may form a light-emittingdevice having the structure shown in any one of FIGS. 4-6, 11, and 12.

In some examples, the one or more additional layers (e.g., chargetransport layer(s) such as hole transport layer and/or electrontransport layer) may be deposited by a method such as, but not limitedto: dip coating, spin coating, spray coating, slot-die process orvarious printing methods such as inkjet printing. These additionallayers may act as transporting, injecting or blocking layers for holesor electrons. The electrode may be formed by a method such as, but notlimited to, sputtering, evaporative coating, printing, chemical vapordeposition, and the like.

The above-described methods are described as providing a single lightemissive device. It will be appreciated that, in some embodiments, thepatterning of the mask may allow for multiple (e.g., an array) oflight-emitting devices to be formed in different regions of thesubstrate. Furthermore, either of the above-described methods can berepeated in order to form light-emitting devices having different QDs(e.g. QDs that emit different colors (e.g. R, G, B)) in differentregions of the substrate, as determined by the patterning of the mask.The arrangement of light-emitting devices may form sub-pixelarrangements, as well as pixel arrangements.

In some embodiments, these light-emitting devices may be arranged suchthat they are separated by one or more insulating materials. Thisarrangement may also be referred to as a “bank structure.” FIGS. 15A and15B show such an exemplary arrangement of light-emitting devices at 500.FIGS. 15A and 15B are not drawn to scale and are used to show thesalient features of the bank structure. As shown, different subpixels400A, 400B are patterned in the same substrate, and the insulatingmaterial 502 delineates the areas where the materials that constitutethe QLED subpixel structures are deposited. FIGS. 15A and 15B show anexemplary arrangement of two light-emitting devices arranged assubpixels. In other embodiments, the subpixel arrangement may includeany suitable number of subpixels (e.g., three, four, etc.). Thedifferent subpixels may be configured to emit light of different colors.

Exemplary insulating materials may include, but are not limited to,polyimides. In some examples, the insulating material may includesurface treatment (e.g. fluorine) in order to modify its wettingproperties (e.g. made hydrophilic to prevent the deposited material fromsticking on the banks and to ensure the subpixel is filled properly).The insulating material 502 forms wells, and the bottoms includedifferent electrodes for each subpixel (e.g., anodes). In the embodimentshown the light-emitting devices include electrodes 104, 106, holetransport layer 112, emissive layer 108, and electron transport layer110 (similar to the arrangement shown in FIG. 6. In other embodiments(not shown) the light-emitting devices of the bank structure may insteadbe similar to the structures of the devices shown in FIG. 1, 4, or 5.The hole transport layer 112 may be deposited commonly or individually(as shown) for the different subpixels. The emissive layers 108 of therespective subpixel 400A, 400B may be sequentially deposited in thedifferent respective subpixel areas. Crosslinking of the emissive layersmay be conducted in accordance with the methods described above. Theelectron transport layer may be deposited commonly or individually (asshown) for the different subpixels. A common top electrode (cathode forstandard structure) is deposited to complete the subpixels structure;although the top electrode is illustrated as a flat layer in FIG. 12A,the structure is not necessarily planar prior to the deposition of saidelectrode.

Example—Production of a Light-Emitting Device

150 nm of ITO is sputtered through a shadow mask onto a 1 mm thick glasssubstrate to define a semi-transparent anode region. PEDOT:PSS inaqueous solution is deposited on top of the anode by spin coating thenbaked at 150° C. to form a hole injection layer. OTPD dissolved inchlorobenzene is deposited on top of the hole injection layer by spincoating then baked at 110° C. to form an hole transport layer. CdSe/CdSquantum dots, OTPD, and a photo initiator are deposited and patterned bythe above-described deposition method shown in FIGS. 13A-13E. ZnOnanoparticles are deposited on top of the emissive layer by spin coatingfrom ethanol followed by baking at 110° C. to form an electron transportlayer. 100 nm of Aluminum is thermally evaporated on top of the electrontransport layer to provide a reflective cathode.

The above-described process yields a light-emitting device having a 1 mmglass substrate, 150 nm ITO anode, 50 nm PEDOT:PSS hole injection layer,40 nm OTPD hole transport layer, 20 nm crosslinked emissive layer havinga OTPD crosslinked matrix within which CdSe/CdS QDs are dispersed, 45 nmZnO electron transport layer, and 100 nm Al cathode.

Although the invention has been shown and described with respect to acertain embodiment or embodiments, it is obvious that equivalentalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification and the annexeddrawings. In particular regard to the various functions performed by theabove described elements (components, assemblies, devices, compositions,etc.), the terms (including a reference to a “means”) used to describesuch elements are intended to correspond, unless otherwise indicated, toany element which performs the specified function of the describedelement (i.e., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary embodiment or embodimentsof the invention. In addition, while a particular feature of theinvention may have been described above with respect to only one or moreof several illustrated embodiments, such feature may be combined withone or more other features of the other embodiments, as may be desiredand advantageous for any given or particular application.

1. A light-emitting device, comprising: an anode; a cathode; and anemissive layer disposed between the anode and the cathode, the emissivelayer comprising quantum dots dispersed in a crosslinked matrix formedfrom one or more crosslinkable charge transport materials, the one ormore crosslinkable charge transport materials comprising an ambipolarmaterial.
 2. The light-emitting device of claim 1, wherein the quantumdots form part of the crosslinked matrix.
 3. The light-emitting deviceof claim 1, wherein the quantum dots comprise ligands having one or morefunctional groups.
 4. The light-emitting device of claim 1, wherein theone or more crosslinkable charge transport material further comprisesone or more hole transport materials.
 5. The light-emitting device ofclaim 1, wherein the one or more crosslinkable charge transport materialfurther comprises one or more electron transport materials.
 6. Thelight-emitting device of claim 1, further comprising a hole transportlayer disposed between the anode and the emissive layer.
 7. Thelight-emitting device of claim 6, wherein the hole transport layer iscrosslinked with the matrix of the emissive layer.
 8. The light-emittingdevice of claim 6, further comprising a hole injection layer disposedbetween the anode and the hole transport layer.
 9. The light-emittingdevice of claim 1, further comprising an electron transport layerdisposed between the cathode and the emissive layer.
 10. Thelight-emitting device of claim 9, wherein the electron transport layeris crosslinked with the matrix of the emissive layer.
 11. The lightemitting device of claim 1, wherein the emissive layer further comprisesone or more photo initiators.
 12. A method of forming an emissive layerof a light-emitting device, comprising: depositing a mixture comprisingquantum dots and one or more crosslinkable charge transport materials ona layer, the one or more crosslinkable charge transport materialscomprising an ambipolar material; and subjecting at least a portion ofthe mixture to UV activation to form an emissive layer comprisingquantum dots dispersed in a crosslinked matrix.
 13. The method of claim12, wherein the quantum dots form part of the crosslinked matrix. 14.The method of claim 12, wherein the quantum dots comprise ligands attheir outer surface.
 15. The method of claim 12, wherein the mixturefurther comprises a photo initiator.
 16. The method of claim 12, whereinthe layer is an electrode.
 17. The method of claim 12, wherein the layeris a hole transport layer.
 18. The method of claim 17, wherein the holetransport layer comprises a crosslinkable hole transport material, andthe UV activation crosslinks the hole transport layer with the matrix ofemissive layer.
 19. The method of claim 12, wherein the layer is anelectron transport layer.
 20. The method of claim 19, wherein theelectron transport layer comprises a crosslinkable electron transportmaterial, and the UV activation crosslinks the electron transport layerwith the matrix of emissive layer.